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N+R_CP_vol1_e_2012_ES5

ISSUE NO 1 9 NEWS & REVIEWS Dr Bart Morlion The awareness of the physiological differences between neuropathic and nociceptive pain and knowledge on the range of specific pharmacological options that are available is still rather low. However, it is recognised that when a neuropathic component is involved, pain is more difficult to treat and often requires the use of combination therapy. There exists a variety of treatment options that target the ascending and/or descending pain pathways in different ways, however not all of them are efficient in every case. Treatments NSAIDs are powerful inhibitors of prostaglandin synthesis and act mainly peripherally. Prostaglandins sensitize peripheral nociceptors. Therefore, NSAIDs primarily treat hyperalgesia or secondary pain, par- ticularly the pain resulting from in- flammation. The role of NSAIDs in the treatment of neuropathic pain is extremely limited. Opioids act by binding to opioid receptors in the CNS and peripheral organs. Opioids reduce pain signal transmission both presynaptically and postsynaptically. Activation of presynaptic opioid receptors inhibits the release of the excitatory neurotransmitters. Postsynaptically, opioid receptor binding hyper- polarizes the membrane thereby reducing the probability of an action potential being generated. Opioids also affect supraspinal structures of pain processing, so that pain is still perceived but no longer experienced as unpleasant or threatening. Neuropathic pain is defined by the International Association for the Study of Pain as “pain initiated or caused by a primary lesion or dys- function in the nervous system”. Ex- amples of neuro-pathic pain conditions include radiculopathy, post-herpetic neuralgia, diabetic polyneuropathy, trigeminal neural- gia, phantom limb pain and spinal cord injury. Today there is also an increasing awareness of a neuro- pathic component in some pain conditions such as cancer pain and chronic low back pain. THE RELEVANCE OF NEUROPATHIC COMPONENTS IN SEVERE CHRONIC PAIN Clinical studies Studies have indicated that 77% of severe chronic back pain patients have a detected neuropathic component and that these patients suffer longer and more severely than those with only nociceptive pain (Freynhagen, 2006)1 . A more recent study has indicated that approximately 4% of the general adult population experienced chronic back pain with a neuropathic component (Schmidt, 2009)2 . This study has also indicated that neuropathic components are more frequent in people with severe back pain compared to people with mild back pain.

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